Implantable prostheses are commonly used to replace or augment body tissue. For example, in the case of the female breast, it sometimes necessary to remove some or all of the mammary gland and surrounding tissue in order to treat breast cancer. This surgery leaves a void that can be filled with an implantable prosthesis. The prosthesis serves to support surrounding tissue and to maintain the appearance of the body. The restoration of the normal appearance of the body has a beneficial psychological effect on post-operative patients, reducing the shock and depression that can often follows extensive surgical procedures. Implantable mammary prostheses are also used more generally for enlargement of the breast. Implantable mammary prostheses are commonly formed of a silicone polymer shell and are filled with saline or some other fluid or gel.
After implantation, collagenous scar tissue generally forms around the implant. This process is commonly referred to as encapsulation. The nature and degree of scar tissue formation is thought to depend on a variety of factors, including: location of the implant, the degree of relative movement between the implant and surrounding tissue, implant size, implant shape, and the surface texture of the implant. In some circumstances, the scar tissue can contract in a process referred to as capsular contracture. This can cause undesirable hardening of the tissue surrounding the implant and can distort the shape of the implant.
For a variety of reasons it can be desirable for an implant such as a soft tissue prosthesis or an implantable sensor to become anchored to surrounding tissue. For example, anchoring can reduce large scale displacement of the implant from the desired location and can reduce relative movement between the implant and surrounding tissue.
Various methods for providing a textured surface to an implantable prosthesis have been described.
Iverson et al. (U.S. Pat. No. 5,964,803 and U.S. Pat. No. 5,525,275) describe an implantable prosthesis having a textured surface formed by depositing a cured polymeric particles on an uncured, tacky surface. This surface on which the particles are deposited is cured and a layer of “uncured elastomeric material” is applied. The entire surface is then cured to create a surface “characterized by a random distribution of peaks separated by valleys.” According to Iverson et al., the “the peaks and valleys are separated by gradual contoured slopes with a smooth transition between the peaks and valleys”. Also according to Iverson et al., the “transitions are substantially free of indentations and interstices which may trap body fluids.”
Ersek et al. (U.S. Pat. No. 4,955,909) describe a molding process that is said to create “a net-like surface grid structure including pillars extending outwardly from a base plane . . . along with indentations or pores being formed in the outer end projecting surfaces of pillars.”
Robert (U.S. Pat. No. 5,296,069) describes creating a textured surface on an implant by pressing a foam sheet against an unvulvanized silicone sheet.
Yan et al. (U.S. Pat. No. 4,960,425) describe implants having a textured surface that “consists of a plurality of substantially microscopic peaks and valleys substantially free of pores or interstices” One of the methods for creating such a surface entails coating a textured mandrel with silicone.
Yan et al. (U.S. Pat. No. 5,022,942) describe implants having a textured surface “formed of non-absorbent material substantially free of pores and interstices”. The surface can be created in a number of ways, including by applying a formable, biocompatible material over at least a portion of the exterior surface of the shell and disposing a texturizing means over the deformable material to imprint a texture on the deformable material.